30 



THE TESTING OF ROAD MATERIALS. 



exactly centered and brought five of the guide rods (/>). As the cross- 

 head (/) continues to rise, the bolts supporting the hammer, which are 



A 



ELEVATION OF HAMMER LIFT AND DEVICE FOFf TAPPING HAMMER 



PLAN OF HAMMER LIFT. 

 J 



FFiONT 



Fi'.. ti. Impart inni-liiiu' to Ifti-niiinc ci-miMitinjr value of rock. 



at an an^lf of about 4." . are thrust open by the sloping head 

 of the adjusting cone rod (/') releasing the hammer, which falls on 



